This application claims the benefit of U.S. Provisional Application No. 61/438,067 filed on Jan. 31, 2011, entitled “Battery Charger Digital Control Circuit and Method,” which application is hereby incorporated herein by reference.
Rechargeable batteries include a variety of types, such as nickel-cadmium (NiCd) batteries, nickel-metal hydride (NiMH) batteries, lithium-ion batteries, lithium-ion polymer batteries, lithium-air batteries, lithium iron phosphate batteries and the like. Rechargeable batteries are used to store electrical energy. On the other hand, a battery charger is employed to charge a rechargeable battery back to a charged state after the rechargeable battery has been depleted.
Different types of rechargeable batteries may employ different charging methods. For example, when a lithium-ion polymer battery is charged from a depleted state to a full charged state, in accordance with the charging profile of lithium-ion polymer batteries, the lithium-ion polymer battery is charged initially at a low current in a pre-conditioning phase. After the voltage of the battery reaches a minimum charge voltage threshold, the battery charging cycle enters a current regulation phase in which the battery is charged at a constant current. In such a current regulation phase, the voltage of the battery keeps rising until the voltage reaches a specified regulation voltage. Subsequently, the battery charging cycle enters a voltage regulation phase by changing the battery charger from a constant current source to a constant voltage source. During the voltage regulation phase, the battery's voltage is held at the specified voltage. Consequently, the charging current gradually decreases. When the charging current is smaller than a specified current value, the battery charging cycle is complete.
Two types of battery chargers are well known and commonly employed. A linear regulator based battery charger comprises an active device acting like a variable resistor. By forcing a voltage drop on the active device, the linear regulator based battery charger can regulate either its output voltage or its output current. On the contrary, a switching regulator based battery charger regulates its output voltage or current by adjusting a duty cycle controlling the turn-on period of a switching element of the charger. In comparison to the linear regulator based battery charger, the switching regulator based battery charger usually provides a high efficiency charging process.
Corresponding numerals and symbols in the different figures generally refer to corresponding parts unless otherwise indicated. The figures are drawn to clearly illustrate the relevant aspects of the various embodiments and are not necessarily drawn to scale.